Although Mycoplasma pneumoniae is a major cause of pneumonia; diagnosis by culture is slow, serodiagnosis presents problems of false positives, and vaccines have been expensive and of moderate effectiveness. The antigenic structure of M. pneumoniae will be studied with emphasis on protein antigens, particular those to which humans mount an antibody response. The goal is characterize these protein antigens and to determine whether strains of M. pneumoniae differ antigenically. Antigenic differences in polypeptide antigens of strains of M. pneumoniae will be determined by comparing 15 strains, one for each year between 1965 and 1980, against human convalescent antiserum collected from the patient that yielded the individual strain. SDS polyacrylamide gel electrophoresis patterns of each strain will be blotted to cellulose nitrate sheets which will be treated with the human sera and developed with peroxidase labelled anti-globulins. The duration of the antibody response will be determined using long-term follow up sera collected from pneumonia patients from whom M. pneumoniae had been isolated. Monospecific and/or monoclonal antibodies will be prepared to polypeptides (to which humans respond) for use in purification of the antigen by immunoadsorption for characterization and for ultimate use in the ELISA test. Both purified, partial purified, and crude antigens will be studied to attempt to develop an ELISA test which effectively measures human antibodies and to attempt to devise a method of detecting M. pneumoniae antigen. M. pneumoniae strains and other Mycoplasma species will be compared by immunoblotting with homologous and heterologous and heterologous rabbit hyperimmune serum to determine taxonomic differences between strains and species. The antigenic specificities of enzymes will be determined to provide for direct well-characterized reagents for classification of Mycoplasma species. Determination of the role of specific protein antigens in infection should provide for more effective and rapid diagnosis and contribute to the eventual prevention of M. pneumoniae infections by immunization.